Bitumen vulcanising composition

ABSTRACT

Provided is a vulcanising agent for vulcanising bitumen, which vulcanising agent comprises a sulphur agent and a binder, wherein the vulcanising agent is in the form of pellets. Further provided is a process for producing a surfacing composition, which process comprises contacting bitumen with an elastomer and the vulcanising agent of the present invention.

[0001] The present invention concerns a composition for vulcanisingbitumen. The bitumen is then useful as a surfacing composition in, forexample, road surfacing. The invention provides a vulcanisingcomposition which when mixed with bitumen and an elastomer gives rise toa composition having improved stability and aging properties. Theinvention also relates to methods for forming the vulcanisingcomposition and road surfacing composition, and to the surfacingcomposition itself.

[0002] It has been known for some time to add elastomeric polymers tobitumen to form a useful road surfacing composition. The elastomerprovides the advantage of allowing the composition to deform underpressure (e.g. when a vehicle is driven across it) and then to return toits original state. This increases the lifetime of the road surface. Ithas also been known for some time to add sulphur or sulphur containingcompounds to such compositions to further strengthen it by introducingcross-linking. This cross-linking is termed vulcanisation. The formationof such compositions is generally carried out in two steps: theelastomer is added to the bitumen and fully dispersed, and then thevulcanising agent is added and cross-linking is allowed to occur. Anumber of published patent applications describe such processes,including WO 98/47966, WO 92/11321, WO 90/02776, WO 93/18092, and WO96/15193.

[0003] A specific process of this type is disclosed in publishedEuropean patent, EP 424 420. This document discloses formation of abitumen composition in two steps. An elastomeric polymer (SBS) isdispersed in bitumen at a temperature of around 140-180° C. When the SBShas fully dispersed in the bitumen, vulcanising agents are added,including sulphur, a sulphur donor and other additives. The mixture isagitated for from 100-150 minutes at a temperature of from 140-180° C.to form the final composition.

[0004] In published French patent application FR 2 737 216 more recentlydeveloped an alternative one-step procedure for forming a surfacingcomposition from bitumen. This method makes use of a preliminary mixtureready for use, which preliminary mixture comprises SBS in powder formand cross-linking agents in powder form. The preliminary mixture isitself thus a powder.

[0005] There are a number of disadvantages associated with all of theabove methods. The two-step processes are more time consuming andrequire separate storage of a larger number of different components.Moreover, the elastomer and cross-linking agent are in powder form andmust be added separately. Thus, their proportions need to be determinedon forming the surfacing composition. This process is prone to errorleading to wastage and increased cost. The one-step process overcomessome of these problems, but is itself associated with further problems.The preliminary mixture is in a powder form and needs to be mixed sinceit is composed of more than one ingredient. Powders are subject tosafety problems, since they are a fire and explosion hazard. This isparticularly problematic for sulphur and sulphur-containing compounds.Moreover, powders are difficult to store and are subject to clogging andcaking which makes them difficult to process.

[0006] An aim of the present invention is to solve the problemsassociated with the above prior art. It is a further aim of the presentinvention to provide a vulcanising composition which is safer, easier touse and gives rise to a final surfacing composition which has improvedstability, storage and aging characteristics and allows a better controlon the amount of product used in the compositions.

[0007] Accordingly, the present invention provides a vulcanising agentfor vulcanising bitumen, which vulcanising agent comprises a sulphuragent and a binder, wherein the vulcanising agent is in the form ofpellets. Generally the sulphur agent is dispersed with the binder. Bypellets, it is meant a product comprising particulate matter collectedtogether to form larger agglomerates. These agglomerates are notespecially limited in shape or size, provided that they are not in ahazardous powder form, and may include an extrudate, tablet or pillformed by extrusion or compression of the vulcanising agent.

[0008] The present invention provides a pelletised vulcanising agentwhich avoids the hazards associated with powders, and can be employed ina one-step process to form a road surfacing agent with an elastomer andbitumen. By one step process is meant a process in which the elastomerand vulcanising agent can be added together to the bitumen, if desired.A two-step process requires that the elastomer and bitumen arethoroughly dispersed before the vulcanising agent is added.Surprisingly, the present vulcanising agent also improves the aging andstability of the surfacing composition in addition to the aboveadvantages.

[0009] The various aspects of the present invention will now bediscussed in more detail.

[0010] The vulcanising agent comprises a binder and a sulphur agent, theproportions of which are not especially limited, provided that thebinder is present in sufficient quantity to allow pellets to be formed.In a preferred embodiment the vulcanising agent comprises 20 wt. % ormore of the binder. More preferably the vulcanising agent comprises from20-90 wt. % of the binder and from 10-80 wt. % of the sulphur agent. Thevulcanising agent may also comprise from 0-30 wt. % of furtheradditives. Preferably the sulphur agent comprises from 10-100 wt. % ofelemental sulphur and from 0-90 wt. % of a sulphur-containing compound.The sulphur agent may thus comprise a sulphur donor, such as zincdibutyl dithiocarbamate (ZDBC) or zinc mercaptobenzothiazol (ZMBT) or asulphinamide. Preferred sulphur containing-compounds and sulphur donorsmay be found in the Rubber Handbook published by the Swedish Institutionof Rubber Technology.

[0011] The binder is not especially limited, provided that it is capableof pelletising the sulphur agent. Preferably, however, the binder has amelting point (and/or softening point) below the melting point ofsulphur, for ease of processing. In preferred embodiments, the bindercomprises a wax, a hydrocarbon resin, a copolymer of ethylene and anacrylic ester. The more preferred binders include polyethylene (PE),glycol monostearate (GMS), ethyl vinyl alcohol (EVA) and copolymers ofethylene and acrylate esters.

[0012] A particularly preferred vulcanising agent is elemental sulphur,and a particularly preferred binder is EVA.

[0013] The vulcanising agent preferably comprises further additives.These additives are not especially limited and may be added to improvemixing and/or facilitate processing. They may also be selected toimprove surface quality, especially road quality. Such further additivesmay comprise tackifiers, elastomers, bitumens, zinc oxide, and/orstearic acid.

[0014] The present invention also provides a process for production ofthe vulcanising agent, which process comprises:

[0015] (a) extruding a sulphur agent with a binder; or

[0016] (b) compressing a sulphur agent with a binder, at a temperaturebelow the melting temperature of the sulphur agent, so as to formpellets of the vulcanisation agent.

[0017] The process is a standard compression or extrusion process and iswell known in the art. Standard processing techniques and devices may beemployed. The process preferably employs a temperature of 110° C. orless, since sulphur melts at around 119° C. However, if the sulphuragent as a whole has a higher melting temperature than this, then highertemperatures may be employed.

[0018] The present invention further provides a process for producing asurfacing composition, which process comprises contacting bitumen withan elastomer and a vulcanising agent as defined above. In a preferredembodiment, the process is carried out at a temperature of 100° C. ormore. More preferably the process is carried out at a temperature of120-200° C. As already mentioned above, this is a one-step process wherethe elastomer and vulcanising agent are added substantiallysimultaneously to the bitumen.

[0019] Generally from 1-15 parts by weight of elastomer are employedwith from 85-99 parts by weight of bitumen. Preferably from 0.01-10 wt.%, more preferably from 0.1-5 wt. % of vulcanising agent is employed,based upon the total weight of bitumen and elastomer.

[0020] The elastomer is not especially limited provided that it has thequalities required for surfacing compositions. Such elastomers are wellknown in the art and are generally rubbery polymers. In a preferredembodiment, the elastomer comprises styrene butadiene styrene (SBS),hydrogenated SBS, styrene isoprene styrene (SIS), styrene ethylenebutadiene styrene (SEBS) and/or polyisobutadiene (PIB).

[0021] The surfacing composition of the present invention has improvedaging and stability properties and is preferably used for producingand/or repairing a road, pavement or track, or other surface forvehicles.

[0022] Typically such surfacing compositions are made up prior totransporting them to the site at which they are to be used. Once made upthey are stored for up to three days at temperatures of around 180° C.,to keep the bitumen from solidifying. Thus, stability at hightemperatures is important for such compositions, and it is importantthat the compositions undergo as little phase separation as possible.The present surfacing compositions are especially stable, as shown inthe ring and ball test (described below) as compared with prior artcompositions.

[0023] The present invention will now be described with reference to thefollowing specific embodiments, which are by way of Example only and arenot intended to limit the invention.

EXAMPLES

[0024] In the following examples, the bitumens employed were aVenezuelan bitumen (Bitumen A) having a penetration of 87 at 25° C., anda Middle Eastern bitumen (Bitumen B) having a penetration of 74 at 25°C. Additionally five chinese bitumen have been tested. They havepenetration values at 25° C. of 75, 58, 78, 83 respectively, for SH1,SH2, SH3 and SH4. The penetration test is a standard well known test inthe industry, in which the depth of penetration of a needle into thebitumen is measured. It was measured here following the methods ofstandard test ASTM D-5-73 revised 95. All these bitumen were used forlaboratory tests.

[0025] The elastomer employed in the laboratory tests was Finaprene® 503(SBS—a 31/69 wt. % styrene/butadiene polymer). The elastomers employedin the industrial road compositions were Finaprene® 503 (SBS—a linear31/69 wt. % styrene/butadiene polymer), Finaprene® 401 (a radial lowmolecular weight 20/80 wt % styrene/butadiene polymer) and Finaprene®411X (a radial high molecular weight 30/70 wt % styrene/butadienepolymer)

[0026] The vulcanising agent comprised either:

[0027] (a) sulphur powder,

[0028] (b) 70/30 wt. % of sulphur/EVA pellets prepared by extrusion; or

[0029] (c) 70/30 wt. % of (80/20 wt. % sulphur/ZDBC)/EVA pelletsprepared by compression.

[0030] (d) 30/62/3/3/2 wt % of EVA/sulphur/ZDBC/ZMBT/PIB pelletsprepared by extrusion

Example 1

[0031] This is an example of the present invention.

[0032] Bitumen A was heated to 180° C. and 3 wt. % of Finaprene® 503 wasadded in pellet form, simultaneously with 0.1 wt. % vulcanisation agent© in pellet form, based on the total weight of bitumen and elastomer.After 120 minutes the mixture was homogeneous. The stability to storagewas good (there was no phase separation) and confirmed the efficacy ofthe vulcanisation.

Example 2

[0033] This is an example of the present invention.

[0034] Bitumen B was heated to 180° C. and 5 wt. % of Finaprene® 503 wasadded in pellet form, simultaneously with 0.1 wt. % vulcanisation agent(b) in pellet form, based on the total weight of bitumen and elastomer.After 120 minutes the mixture was homogeneous. The stability to storagewas good (there was no phase separation) and confirmed the efficacy ofthe vulcanisation.

Example 3

[0035] This is a comparative example employing a method of FR 2 737 216.

[0036] Bitumen B was heated to 180° C. and 5 wt. % of Finaprene® 503 wasadded in powder form, simultaneously with 0.1 wt. % vulcanisation agent(a) in powder form, based on the total weight of bitumen and elastomer.After 120 minutes the mixture was homogeneous. The stability to storagewas less good than for Examples 1 and 2.

[0037] Stability and Aging Test Using the Ring and Ball Method.

[0038] The products of Example 2 and Comparative Example 3 were testedfor stability. An internal standard method developed from the ring andball method (ASTM-D36) was employed. The surfacing composition is coatedon a ring after it has been made, then the ring is submerged in hot oil.The temperature at which the composition falls away from the ring isrecorded. The composition is stored at high temperature for 3 days andthe method is repeated. If the stability is good, the composition willretain its tackiness and the temperature will ideally remain as close tothe originally measured temperature as possible. The larger the drop intemperature, the lower the stability of the composition and the worseits aging characteristics.

[0039] The results for the compositions formed in Examples 2 and 3 areshown below in Table 1. TABLE 1 Drop in temp/° C. Mixing time/minsExample 2 Example 3 120 7 10 180 5 10

[0040] Table 1 shows that for mixing times of 2 and 3 hours, there is alesser drop in temperature for the composition of the present inventioncompared with the closest prior art composition. This highlights theimprovement in aging and stability characteristics of the presentcompositions.

Examples 4 to 7

[0041] In these examples, several surfacing compositions were preparedfrom the Chinese Bitumens SH1, SH2, SH3 and SH4, with various elastomersin different amounts and optionally with various amounts of heavyfurfurol extract. The compositions according to the present inventionwere prepared with 0.1 wt % of vulcanising agent d) in pellet form andthe comparative examples were prepared without vulcanising agent. Thecompositions and results are displayed in Tables 2 to 5. In theseexamples, the ductility was measured following the method of standardtest IP 32/55, the kinematic viscosity of asphalt was measured followingthe method of standard test ASTM D 2170 and the elastic recovery wasmeasured following the method of standard test DIN V 52021-1. TABLE 2Bitumen SH1. Composition wt % wt % wt % Bitumen SH1 96.5 96.4 95.5Finaprene ® 503 — — — Finaprene ® 401 3.5 3.5 4.5 Vulcanising agent —0.1 — Heavy furfurol extract — — — Properties Ring and balltemperature-° C. 68 70 80 Penetration  5° C.-{fraction (1/10)} mm 10 1113  15° C.-{fraction (1/10)} mm 18 20 18  25° C.-{fraction (1/10)} mm 5155 54 Viscosity 135° C.-Pa · s 1.22 1.47 1.54 150° C.-Pa · s 0.72 0.840.89 Ductility  5° C.-cm 13 14 20  13° C.-cm 60 80 60  25° C.-cm 62 8758 Elastic recovery-% 92 95 97 Storage stability (48 hrs at no yes no163° C.)

[0042] TABLE 3 Bitumen SH2. Composition wt % wt % wt % wt % wt % BitumenSH2 97.5 97.4 96.5 96.4 95.5 Finaprene ® 503 — — — — — Finaprene ® 4012.5 2.5 3.5 3.5 4.5 Vulcanising agent — 0.1 — 0.1 — Heavy furfurolextract — — — — — Properties Ring and ball temperature −° C. 53 55 67 6974 Penetration 5° C.-1/10 mm 9 10 9 10 9 15° C.-1/10 mm 16 10 15 17 1625° C.-1/10 mm 47 44 43 51 44 Viscosity 135° C.-Pa.s 1.16 1.16 1.31 1.521.76 150° C.-Pa.s 0.63 0.70 0.79 0.85 0.98 Ductility 5° C.-cm 6 1 8 8 1413° C.-cm 24 41 52 58 60 25° C.-cm 97 >130 54 82 53 Elastic recovery-%35 58 93 93 98 Storage stability (48 hrs at no yes no yes No 163° C.)

[0043] TABLE 4 Bitumen SH3. Composition Wt % wt % wt % wt % wt % wt % wt% wt % wt % wt % wt % wt % Bitumen SH3 96.5 96.4 95.5 97.5 97.4 97.597.5 96.5 96.4 96.5 96.5 95.5 Finaprene ® 503 3.5 3.5 4.5 — — — — — — —— — Finaprene ® 401 — — — 2.5 2.5 2.5 2.5 3.5 3.5 3.5 3.5 4.5Vulcanising agent — 0.1 — — 0.1 — — — 0.1 — — — Heavy furfurol extract —— — — — 5% 10% — — 5% 10% — Properties Ring and ball temperature-° C. 5254 93 50 52 48 45 70 72 65 58 76 Penetration 5° C.-1/10 mm 13 12 11 1110 — — 10 12 — — 10 15° C.-1/10 mm 22 23 22 21 20 — — 21 21 — — 21 25°C.-1/10 mm 57 60 53 66 60 88 124 58 57 74 110 53 Viscosity 135° C.-Pa.s1.03 1.12 1.28 0.89 0.99 0.86 0.67 1.18 1.30 0.95 0.79 1.51 150° C.-Pa.s0.63 0.66 0.79 0.55 0.59 — — 0.67 0.78 — — 0.82 Ductility 5° C.-cm 20 3239 11 11 22 57 22 19 46 77 26 13° C.-cm 71 73 102 37 54 — — 49 74 — — 6625° C.-cm >140 >140 103 110 >130 — — 52 65 — — 52 Elastic recovery-% 6868 98 28 60 65 58 98 95 95 95 100 Storage stability (48 hrs at no yes noyes Yes yes yes no yes yes yes no 163° C.)

[0044] TABLE 5 Bitumen SH4. Composition wt % wt % wt % wt % wt % wt %Bitumen SH4 97 96.9 96.5 96.4 96 95.9 Finaprene ® 503 — — — — — —Finaprene ® 401 3 3 3.5 3.5 4 4 Vulcanising agent — 0.1 — 0.1 — 0.1Properties Ring and ball Tempera- 57 59 73 74 80 82 ture-° C.Penetration 5° C.-1/10 mm 10 12 14 11 11 11 15° C.-1/10 mm 23 20 22 2319 19 25° C.-1/10 mm 68 57 43 6 58 55 Viscosity 135° C.-Pa.s 1.00 1.161.09 1.10 1.2 1.47 150° C.-Pa.s 0.61 0.65 0.72 0.77 0.74 0.86 Ductility5° C.-cm 15 21 16 41 25 27 13° C.-cm 46 51 70 96 72 84 25° C.-cm 54 10955 7 56 70 Elastic recovery-% 78 73 95 98 98 98 Storage stability (48hrs at yes yes no yes no Yes 163° C.)

[0045] The results displayed in Tables 2 to 5 clearly show that all thebitumen compositions prepared according to the present inventions hadexcellent storage stability. In addition, as desired, the ring and balltemperature was higher for the compositions of the present invention.The viscosity was also higher for the compositions using the vulcanisingagent of the invention resulting in a better cohesion and so was theductility. It must be observed in Table 4 that a higher ductility can beobtained by the addition of 5 to 10 wt % of heavy furfurol extract, butat the expense of the ring and ball temperature that is lower and at theexpense of the penetration value that is higher.

INDUSTRIAL EXAMPLES

[0046] Two road compositions have been prepared with the Chinese bitumenSH2, the elastomer Finaprene® 503 and the vulcanising composition d) inpellet form and in powder form respectively. The small drop intemperature observed for the laboratory tests of Examples 1 and 2 wasconfirmed for the industrial examples. This can be seen in Table 6showing the drop in ring and ball temperature as a function of ageingfor the same vulcanising agent in pellet form and in powder form. TABLE6 Difference in Ring and Ball Temperature after ageing. Vulcanisingagent ΔT ° C. Pellets Powder 1 day at 180° C. 2.3 5.6 2 days at 180° C.3.3 6.0 3 days at 180° C. 3.3 5.7

1. A vulcanising agent for vulcanising bitumen, which vulcanising agentcomprises a sulphur agent and a binder, wherein the vulcanising agent isin the form of pellets.
 2. A vulcanising agent according to claim 1,comprising: (i) 20-90 wt. % of the binder; and (ii) 10-80 wt. % of thesulphur agent; and (iii) 0-30 wt. % of additives.
 3. A vulcanising agentaccording to claim 1 or claim 2, wherein the sulphur agent comprisesfrom 10-100 wt. % of elemental sulphur and from 0-90 wt. % of asulphur-containing compound.
 4. A vulcanising agent according to anypreceding claim, wherein the sulphur agent comprises a sulphur donor. 5.A vulcanising agent according to claim 4, wherein the sulphur donorcomprises zinc dibutyl dithiocarbamate (ZDBC).
 6. A vulcanising agentaccording to any preceding claim, wherein the binder comprises a wax, ahydrocarbon resin, a copolymer of ethylene and an acrylic ester,polyethylene (PE), glycol monostearate (GMS) and/or ethyl vinyl alcohol(EVA).
 7. A vulcanising agent according to any preceding claim, whereinthe additives comprise a tackifier, an elastomer, bitumen, zinc oxideand/or stearic acid.
 8. A vulcanising agent according to any precedingclaim, wherein the pellets are in the form of an extrudate, tablet orpill formed by extrusion or compression of the vulcanising agent.
 9. Aprocess for production of a vulcanising agent, which process comprises:(a) extruding a sulphur agent with a binder; or (b) compressing asulphur agent with a binder, at a temperature below the meltingtemperature of the sulphur agent, so as to form pellets of thevulcanisation agent.
 10. A process according to claim 9, wherein thetemperature is a temperature of 110° C. or less.
 11. A process accordingto claim 9 or claim 10, wherein the vulcanising agent comprises an agentas defined in any of claims 2-8.
 12. A vulcanising agent obtainableaccording to a process as defined in any of claims 9-11.
 13. A processfor producing a surfacing composition, which process comprisescontacting bitumen with an elastomer and a vulcanising agent as definedin any of claims 1-8 and
 12. 14. A process according to claim 13,wherein the contacting is carried out at a temperature of 100° C. ormore.
 15. A process according to claim 14, wherein the contacting iscarried out at a temperature of 120-200° C.
 16. A process according toany of claims 13-15, wherein from 1-10 parts by weight of elastomer areemployed with from 90-99 parts by weight of bitumen.
 17. A processaccording to any of claims 13-16 wherein from 0.01-10 wt, % ofvulcanising agent is employed, based upon the total weight of bitumenand elastomer.
 18. A process according to any of claims 13-17, whereinthe elastomer comprises styrene butadiene styrene (SBS), hydrogenatedSBS, styrene isoprene styrene (SIS), styrene ethylene butadiene styrene(SEBS) and/or polyisobutadiene (PIB).
 19. A surfacing compositionobtainable according to a process as defined in any of claims 13-18. 20.Use of the vulcanising agent in the form of pellets of the presentinvention to reduce health hazards.
 20. Use of a surfacing compositionas defined in claim 19 for producing and/or repairing a road, pavementor track, or other surface for vehicles.
 21. Use of a surfacingcomposition as defined in claim 19 in roofing compositions andmembranes, waterproof bitumen compositions membranes or mastics, jointsealants, or sound deadening or sound proofing compositions ormembranes.